Staring with my buddy in Arvada:
Rogue 2x3 squat stand with spotter arms
Rogue Flat Bench
Rogue Boneyard Ohio Power Bar - great knurling
Rep Fitness - Bumper Plates - 45-35-25
Standard Barbell - Change Plates - 10-5-2.5
Dumbbells in a few different sizes
Alan Thrall's Home Gym:
Rogue Squat stands
Marcy Flat Bench
Beater Bar (20kg)
Beater Bar (15kg)
Adjustable Dumbbell Handles
Steel Plates ~500 pounds
Long story short is that you do not need a large space or a lot of money to set up a great supplemental or primary gym space.
My bare bones gym would include:
Crossover Symmetry - Red and Purple Bands $50 new
Folding Rack with Pull-up Bar - $300-$400 used
20kg Barbell ($50 used) and 6x45, 2x25, 2x15, 2x10 bumper plates (370#, $500 used) and 2x5, 2x2.5 steel plates (15#, $40 used)
2 Stall Mats - $100 new
35# DB pair - $100 used
Flat Bench - $100 used
2 abmat - $50 new
$1390 and I could park a car in the garage.
I could get away with less weight for a supplemental gym. I could substitute a variety of items for a rack. I just need to be able to bench and squat. Everything else takes up very little room.
My garage gym feels tight due to the Back Extension, Ab Bench and Titan Storage Unit (which holds bumper plates, wall balls, ab mats and dumbbells. I am not ready to part with any of those items.